An adaptable mesocosm platform for performing integrated assessments of nanomaterial risk in complex environmental systems

Impacts of Differentially Shaped Silver Nanoparticles with Increasingly Complex Hydrophobic Thiol Surface Coatings in Small-Scale Laboratory Microcosms

We investigated the impacts of spherical and triangular-plate-shaped lipid-coated silver nanoparticles (AgNPs) designed to prevent surface oxidation and silver ion (Ag+) dissolution in a small-scale microcosm to examine the role of shape and surface functionalization on biological interactions. Exposures were conducted in microcosms consisting of algae, bacteria, crustaceans, and fish embryos. Each microcosm was exposed to one of five surface chemistries within each shape profile (at 0, 0.1, or 0.5 mg Ag/L) to investigate the role of shape and surface composition on organismal uptake and toxicity. The hybrid lipid-coated AgNPs did not result in any significant release of Ag+ and had the most significant toxicity to D. magna, the most sensitive species, although the bacterial population growth rate was reduced in all exposures. Despite AgNPs resulting in increasing algal growth over the experiment, we found no correlation between algal growth and the survival of D. magna, suggesting that the impacts of the AgNPs on bacterial survival influenced algal growth rates. No significant impacts on zebrafish embryos were noted in any exposure. Our results demonstrate that the size, shape, and surface chemistry of AgNPs can be engineered to achieve specific goals while mitigating nanoparticle risks.

Tritiated stainless steel (nano)particle release following a nuclear dismantling incident scenario: Significant exposure of freshwater ecosystem benthic zone

Nuclear facilities continue to be developed to help meet global energy demands while reducing fossil fuel use. However, an incident during the dismantling of these facilities could accidentally release tritiated particles (e.g. stainless steel) into the environment. Herein, we investigated the environmental dosimetry, fate, and impact of tritiated stainless steel (nano)particles (1 mg.L-1 particles and 1 MBq.L-1 tritium) using indoor freshwater aquatic mesocosms to mimic a pond ecosystem. The tritium (bio)distribution and particle fate and (bio)transformation were monitored in the different environmental compartments over 4 weeks using beta counting and chemical analysis. Impacts on picoplanktonic and picobenthic communities, and the benthic freshwater snail, Anisus vortex, were assessed as indicators of environmental health. Following contamination, some tritium (∼16%) desorbed into the water column while the particles rapidly settled onto the sediment. After 4 weeks, the particles and the majority of the tritium (>80%) had accumulated in the sediment, indicating a high exposure of the benthic ecological niche. Indeed, the benthic grazers presented significant behavioral changes despite low steel uptake (<0.01%). These results provide knowledge on the potential environmental impacts of incidental tritiated (nano)particles, which will allow for improved hazard and risk management.

Biotic and Abiotic Interactions in Freshwater Mesocosms Determine Fate and Toxicity of CuO Nanoparticles

Transformation, dissolution, and sorption of copper oxide nanoparticles (CuO-NP) play an important role in freshwater ecosystems. We present the first mesocosm experiment on the fate of CuO-NP and the dynamics of the zooplankton community over a period of 12 months. Increasingly low (0.08-0.28 mg Cu L-1) and high (0.99-2.99 mg Cu L-1) concentrations of CuO-NP and CuSO4 (0.10-0.34 mg Cu L-1) were tested in a multiple dosing scenario. At the high applied concentration (CuO-NP_H) CuO-NP aggregated and sank onto the sediment layer, where we recovered 63% of Cu applied. For the low concentration (CuO-NP_L) only 41% of applied copper could be recovered in the sediment. In the water column, the percentage of initially applied Cu recovered was on average 3-fold higher for CuO-NP_L than for CuO-NP_H. Zooplankton abundance was substantially compromised in the treatments CuSO4 (p < 0.001) and CuO-NP_L (p < 0.001). Community analysis indicated that Cladocera were most affected (bk = -0.49), followed by Nematocera (bk = -0.32). The abundance of Cladocera over time and of Dixidae in summer was significantly reduced in the treatment CuO-NP_L (p < 0.001; p < 0.05) compared to the Control. Our results indicate a higher potential for negative impacts on the freshwater community when lower concentrations of CuO-NP (<0.1 mg Cu L-1) enter the ecosystem.

Fate and effects of microplastics in combination with pharmaceuticals and endocrine disruptors in freshwaters: Insights from a microcosm experiment

Microplastic contamination of freshwater ecosystems has become an increasing environmental concern. To advance the hazard assessment of microplastics, we conducted a microcosm experiment in which we exposed a simplified aquatic ecosystem consisting of moss and caddisflies to microplastics (polyethylene, polystyrene and polypropylene) and pharmaceuticals and personal care products (1H-benzotriazole, bisphenol A, caffeine, gemfibrozil, ketoprofen, methylparaben, estriol, diphenhydramine, tris (1-chloro-2-propyl) phosphate) over the course of 60 days. We monitored the flux of microplastics within the microcosm, as well as the metabolic and total protein variation of organisms. This study offers evidence highlighting the capacity of moss to act as a sink for free-floating microplastics in freshwater environments. Moss is also shown to serve as a source and pathway for microplastic particles to enter aquatic food webs via caddisflies feeding off of the moss. Although most ingested microparticles were eliminated between caddisflies life stages, a small fraction of microplastics was transferred from aquatic to terrestrial ecosystem by emergence. While moss exhibited a mild response to microplastic stress, caddisflies ingesting microplastics showed stress comparable to that caused by exposure to pharmaceuticals. The molecular responses that the stressors triggered were tentatively identified and related to phenotypic responses, such as the delayed development manifested through the delayed emergence of caddisflies exposed to stress. Overall, our study provides valuable insights into the adverse effects of microplastics on aquatic species, compares the impacts of microplastics on freshwater biota to those of pharmaceuticals and endocrine disrupting compounds, and demonstrates the role aquatic organisms have in redistributing microplastics between aquatic and terrestrial ecosystems.

Bacterial Metabolites and Particle Size Determine Cerium Oxide Nanomaterial Biotransformation

Soil is a major receptor of manufactured nanomaterials (NMs) following unintentional releases or intentional uses. Ceria NMs have been shown to undergo biotransformation in plant and soil organisms with a partial Ce(IV) reduction into Ce(III), but the influence of environmentally widespread soil bacteria is poorly understood. We used high-energy resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS) with an unprecedented detection limit to assess Ce speciation in a model soil bacterium (Pseudomonas brassicacearum) exposed to CeO₂ NMs of different sizes and shapes. The findings revealed that the CeO₂ NM's size drives the biotransformation process. No biotransformation was observed for the 31 nm CeO₂ NMs, contrary to 7 and 4 nm CeO₂ NMs, with a Ce reduction of 64 ± 14% and 70 ± 15%, respectively. This major reduction appeared quickly, from the early exponential bacterial growth phase. Environmentally relevant organic acid metabolites secreted by Pseudomonas, especially in the rhizosphere, were investigated. The 2-keto-gluconic and citric acid metabolites alone were able to induce a significant reduction in 4 nm CeO₂ NMs. The high biotransformation measured for <7 nm NMs would affect the fate of Ce in the soil and biota.

The curious case of methylparaben: Anthropogenic contaminant or natural origin?

The widespread use of methylparaben as a preservative has caused increased exposure to natural aquatic systems in recent decades. However, current studies have suggested that exposure to this compound can result in endocrine disrupting effects, raising much concern regarding its environmental impact. In contast, methylparaben has also been found to be part of the metabolome of some organisms, prompting the question as to whether this compound may be more natural than previously assumed. Through a combination of field studies investigating the natural presence of methylparaben across different taxa, and a 54-day microcosm experiment examining the bioaccumulation and movement of methylparaben across different life stages of aquatic insects (order Trichoptera), our results offer evidence suggesting the natural origin of methylparaben in aquatic and terrestrial biota. This study improves our understanding of the role and impact this compound has on biota and challenges the current paradigm that methylparaben is exclusively a harmful anthropogenic contaminant. Our findings highlight the need for further research on this topic to fully understand the origin and role of parabens in the environment which will allow for a comprehensive understanding of the extent of environmental contamination and result in a representative assessment of the environmental risk that may pose.

Aquatic Mesocosm Strategies for the Environmental Fate and Risk Assessment of Engineered Nanomaterials

In the past decade, mesocosms have emerged as a useful tool for the environmental study of engineered nanomaterials (ENMs) as they can mimic the relevant exposure scenario of contamination. Herein, we analyzed the scientific outcomes of aquatic mesocosm experiments, with regard to their designs, the ENMs tested, and the end points investigated. Several mesocosm designs were consistently applied in the past decade to virtually mimic various contamination scenarios with regard to ecosystem setting as well as ENMs class, dose, and dosing. Statistical analyses were carried out with the literature data to identify the main parameters driving ENM distribution in the mesocosms and the potential risk posed to benthic and planktonic communities as well as global ecosystem responses. These analyses showed that at the end of the exposure, mesocosm size (water volume), experiment duration, and location indoor/outdoor had major roles in defining the ENMs/metal partitioning. Moreover, a higher exposure of the benthic communities is often observed but did not necessarily translate to a higher risk due to the lower hazard posed by transformed ENMs in the sediments (e.g., aggregated, sulfidized). However, planktonic organisms were generally exposed to lower concentrations of potentially more reactive and toxic ENM species. Hence, mesocosms can be complementary tools to existing standard operational procedures for regulatory purposes and environmental fate and risk assessment of ENMs. To date, the research was markedly unbalanced toward the investigation of metal-based ENMs compared to metalloid- and carbon-based ENMs but also nanoenabled products. Future studies are expected to fill this gap, with special regard to high production volume and potentially hazardous ENMs. Finally, to take full advantage of mesocosms, future studies must be carefully planned to incorporate interdisciplinary approaches and ensure that the large data sets produced are fully exploited.

MESOCOSM: A mesocosm database management system for environmental nanosafety

Engineered nanomaterials (ENMs) are intentionally designed and produced by humans to revolutionize the manufacturing sector, such as electronic goods, paints, tires, clothes, cosmetic products, and biomedicine. With the spread of these ENMs in our daily lives, scientific research have generated a huge amount of data related to their potential impacts on human and environment health. To date, these data are gathered in databases mainly focused on the (eco)toxicity and occupational exposure to ENMs. These databases are therefore not suitable to build well-informed environmental exposure scenarios covering the life cycle of ENMs. In this paper, we report the construction of one of the first centralized mesocosm database management system for environmental nanosafety (called MESOCOSM) containing experimental data collected from mesocosm experiments suited for understanding and quantifying both the environmental hazard and exposure. The database, which is publicly available through https://aliayadi.github.io/MESOCOSM-database/, contains 5200 entities covering tens of unique experiments investigating Ag, CeO₂, CuO, TiO₂-based ENMs as well as nano-enabled products. These entities are divided into different groups i.e. physicochemical properties of ENMS, environmental, exposure and hazard endpoints, and other general information about the mesocosm testing, resulting in more than forty parameters in the database. The MESOCOSM database is equipped with a powerful application, consisting of a graphical user interface (GUI), allowing users to manage and search data using complex queries without relying on programmers. MESOCOSM aims to predict and explain ENMs behavior and fate in different ecosystems as well as their potential impacts on the environment at different stages of the nanoproducts lifecycle. MESOCOSM is expected to benefit the nanosafety community by providing a continuous source of critical information and additional characterization factors for predicting ENMs interactions with the environment and their risks.

The Known and Unknown about the Environmental Safety of Nanomaterials in Commerce

The widespread nanomaterial use in commercial products has fed significant concern over environmental health and safety ramifications. Initially, little was known as to how these highly reactive particulates interacted with biological systems. Nanomaterials have introduced complexities not normally considered in traditional safety assessments of chemicals and therefore have generated uncertainty in the reliability of standard tests of safety. Advances in understanding the potential impacts of nanomaterials have occurred since their introduction, particularly for those used in the greatest quantities in commerce. The impact of characteristics such as charge, size, surface functionalization, chemical composition, and certain transformations on the potential effect of nanomaterials in the environment continue to move the field forward. However, generalizations of risk based on any one factor across nanomaterials is not possible. Estimating risk also remains difficult due to the introduction of materials that are new and more complex, minimal information on the specific molecular interactions of nanomaterials and organisms, and the need for more tools for measuring the dynamics of nanomaterial state and fate in complex matrices. Finally, exposure estimates are difficult due to difficulty of environmental monitoring which may be exacerbated by lack of information on nanomaterials in products and new uses in the marketplace.

Marine sediment toxicity: A focus on micro- and mesocosms towards remediation

Micro- and/or mesocosms are experimental tools bringing ecologically relevant components of the natural environment under controlled conditions closest to the real world, without losing the advantage of reliable reference conditions and replications, providing a link between laboratory studies and filed studies in natural environments. Here, for the first time, a formal comparison of different types of mesocosm applied to the study of marine contaminants is offered, considering that pollution of coastal areas represented a major concern in the last decades because of the abundance of discharged toxic substances. In particular, the structural characteristics of micro- and mesocosms (m-cosms) used to study marine contaminated sediments were reviewed, focusing on their advantages/disadvantages. Their potentiality to investigate sediment remediation have been discussed, offering new perspective on how the use of m-cosms can be useful for the development of practical application in the development of solutions for contaminated sediment management in the contaminated marine environment.

Natural molecule coatings modify the fate of cerium dioxide nanoparticles in water and their ecotoxicity to Daphnia magna

The ongoing development of nanotechnology has raised concerns regarding the potential risk of nanoparticles (NPs) to the environment, particularly aquatic ecosystems. A relevant aspect that drives NP toxicity is represented by the abiotic and biotic processes occurring in natural matrices that modify NP properties, ultimately affecting their interactions with biological targets. Therefore, the objective of this study was to perform an ecotoxicological evaluation of CeO₂NPs with different surface modifications representative of NP bio-interactions with molecules naturally occurring in the water environment, to identify the role of biomolecule coatings on nanoceria toxicity to aquatic organisms. Ad hoc synthesis of CeO₂NPs with different coating agents, such as Alginate and Chitosan, was performed. The ecotoxicity of the coated CeO₂NPs was assessed on the marine bacteria Aliivibrio fischeri, through the Microtox® assay, and with the freshwater crustacean Daphnia magna. Daphnids at the age of 8 days were exposed for 48 h, and several toxicity endpoints were evaluated, from the molecular level to the entire organism. Specifically, we applied a suite of biomarkers of oxidative stress and neurotoxicity and assessed the effects on behaviour through the evaluation of swimming performance. The different coatings affected the hydrodynamic behaviour and colloidal stability of the CeO₂NPs in exposure media. In tap water, NPs coated with Chitosan derivative were more stable, while the coating with Alginate enhanced the aggregation and sedimentation rate. The coatings also significantly influenced the toxic effects of CeO₂NPs. Specifically, in D. magna the CeO₂NPs coated with Alginate triggered oxidative stress, while behavioural assays showed that CeO₂NPs coated with Chitosan induced hyperactivity. Our findings emphasize the role of environmental modification in determining the NP effects on aquatic organisms.

Aqueous aging of a silica coated TiO2 UV filter used in sunscreens: investigations at the molecular scale with dynamic nuclear polarization NMR

Short-term, aqueous aging of a commercial nanocomposite TiO₂ UV filter with a protective SiO₂ shell was examined in abiotic simulated fresh- and seawater. Under these conditions, the SiO₂ layer was quantitatively removed (∼88–98%) within 96 hours, as determined using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). While these bulk ICP-AES analyses suggested almost identical SiO₂ shell degradation after aging in fresh- and seawater, surface sensitive ²⁹Si dynamic nuclear polarization (DNP) solid-state nuclear magnetic resonance (SSNMR), with signal enhancements of 5–10× compared to standard SSNMR, was able to distinguish differences in the aged nanocomposites at the molecular level. DNP-SSNMR revealed that the attachment of the silica layer to the underlying TiO₂ core rested on substantial Si–O–Ti bond formation, bonds which were preserved after freshwater aging, yet barely present after aging in seawater. The removal of the protective SiO₂ layer is due to ionic strength accelerated dissolution, which could present significant consequences to aqueous environments when the photoactive TiO₂ core becomes exposed. This work demonstrates the importance of characterizing aged nanocomposites not only on the bulk scale, but also on the molecular level by employing surface sensitive techniques, such as DNP-NMR. Molecular level details on surface transformation and elemental speciation will be crucial for improving the environmental safety of nanocomposites.

Short-term, aqueous aging of a commercial nanocomposite TiO₂ UV filter with a protective SiO₂ shell was examined in abiotic simulated fresh- and seawater.

Assessment of Cu and CuO nanoparticle ecological responses using laboratory small-scale microcosms

Copper based nanoparticles (NPs) are used extensively in industrial and commercial products as sensors, catalysts, surfactants, antimicrobials, and for other purposes. The high production volume and increasing use of copper-based NPs make their ecological risk a concern. Commonly used copper-based NPs are composed of metallic copper or copper oxide (Cu and CuO NPs); however, their environmental toxicity can vary dramatically depending on their physico-chemical properties, such as dissolution, aggregation behavior, and the generation of reactive oxygen species. Here, we investigated the NP dissolution, organismal uptake and aquatic toxicity of Cu and CuO NPs at 0, 0.1, 1, 5 or 10 mg Cu/L using a previously developed multi-species microcosm. This 5-day microcosm assay was comprised of C. reinhardtti, E. coli, D. magna, and D. rerio. We hypothesized that Cu and CuO NPs can elicit differential toxicity to the organisms due to alterations in particle dissolution and variations in organismal uptake. The actual concentrations of dissolved Cu released from the NPs were compared to ionic copper controls (CuCl₂) at the same concentrations to determine the relative contribution of particulate and dissolved Cu on organism uptake and toxicity. We found that both NPs had higher uptake in D. magna and zebrafish than equivalent ionic exposures, suggesting that both Cu-based NPs are taken up by organisms. Cu NP exposures significantly inhibited algal growth rate, D. magna survival, and zebrafish hatching while exposure to equivalent concentrations of CuCl₂ (dissolved Cu fraction) and CuO NPs did not. This indicates that Cu NPs themselves likely elicited a particle-specific mechanism of toxicity to the test organisms, or a combination effect from ionic Cu and the Cu NPs. Overall, this work was the first study to utilize a small-scale rapid assay designed to evaluate the fate and ecotoxicological impacts of Cu and CuO NPs in a mixed aquatic community.

Engineered nanomaterials: From their properties and applications, to their toxicity towards marine bivalves in a changing environment

As a consequence of their unique characteristics, the use of Engineered Nanomaterials (ENMs) is rapidly increasing in industrial, agricultural products, as well as in environmental technology. However, this fast expansion and use make likely their release into the environment with particular concerns for the aquatic ecosystems, which tend to be the ultimate sink for this type of contaminants. Considering the settling behaviour of particulates, benthic organisms are more likely to be exposed to these compounds. In this way, the present review aims to summarise the most recent data available from the literature on ENMs behaviour and fate in aquatic ecosystems, focusing on their ecotoxicological impacts towards marine and estuarine bivalves. The selection of ENMs presented here was based on the OECD's Working Party on Manufactured Nanomaterials (WPMN), which involves the safety testing and risk assessment of ENMs. Physical-chemical characteristics and properties, applications, environmental relevant concentrations and behaviour in aquatic environment, as well as their toxic impacts towards marine bivalves are discussed. Moreover, it is also identified the impacts derived from the simultaneous exposure of marine organisms to ENMs and climate changes as an ecologically relevant scenario.

Monitoring the Environmental Aging of Nanomaterials: An Opportunity for Mesocosm Testing?

Traditional aging protocols typically examine only the effects of a limited number of stresses, and relatively harsh conditions may trigger degradation mechanisms that are not observed in actual situations. Environmental aging is, in essence, the complex interaction of multiple mechanical, physicochemical and biological stresses. As yet, there is no (pre)standardized procedure that addresses this issue in a satisfactory manner. Mesocosm experiments can be designed to specifically cover the aging of nanomaterials while characterizing the associated exposure and hazard. The scenario of exposure and the life time of the nanomaterial appear as the predominant factors in the design of the experiment, and appropriate precautions need to be taken. This should the subject of guidance that may be divided into product/application categories.

Safety Assessment of Graphene-Based Materials: Focus on Human Health and the Environment

Graphene and its derivatives are heralded as "miracle" materials with manifold applications in different sectors of society from electronics to energy storage to medicine. The increasing exploitation of graphene-based materials (GBMs) necessitates a comprehensive evaluation of the potential impact of these materials on human health and the environment. Here, we discuss synthesis and characterization of GBMs as well as human and environmental hazard assessment of GBMs using in vitro and in vivo model systems with the aim to understand the properties that underlie the biological effects of these materials; not all GBMs are alike, and it is essential that we disentangle the structure-activity relationships for this class of materials.

Gold nanoparticle biodissolution by a freshwater macrophyte and its associated microbiome

Predicting nanoparticle fate in aquatic environments requires mimicking of ecosystem complexity to observe the geochemical processes affecting their behaviour. Here, 12 nm Au nanoparticles were added weekly to large-scale freshwater wetland mesocosms. After six months, ~70% of Au was associated with the macrophyte Egeria densa, where, despite the thermodynamic stability of Au⁰ in water, the pristine Au⁰ nanoparticles were fully oxidized and complexed to cyanide, hydroxyls or thiol ligands. Extracted biofilms growing on E. densa leaves were shown to dissolve Au nanoparticles within days. The Au biodissolution rate was highest for the biofilm with the lowest prevalence of metal-resistant taxa but the highest ability to release cyanide, known to promote Au⁰ oxidation and complexation. Macrophytes and the associated microbiome thus form a biologically active system that can be a major sink for nanoparticle accumulation and transformations. Nanoparticle biotransformation in these compartments should not be ignored, even for nanoparticles commonly considered to be stable in the environment.

Silver nanoparticles in seawater: A dynamic mass balance at part per trillion silver concentrations

This study investigates the dynamic processes affecting silver (Ag) nanoparticles that have been spiked into seawater at environmentally relevant concentrations (200 and 2000ngAgL^-1). Seawater samples were taken at regular time intervals from multiple microcosm tanks and analysed rapidly, without any sample preparation, using a recently developed flow injection on-line dilution single particle inductively coupled plasma mass spectrometry method. Dissolution was found to be the predominant process of Ag nanoparticle transformation, with its rate being influenced by the type and thickness of the nanoparticle organic coating. More specifically the branched poly(ethyleneimine) coating provided additional stability to the 40 and 60nmAg nanoparticles that were tested, compared to the poly(vinylpyrrolidone) coated ones. At high Ag nanoparticle spiking levels and after 24h of exposure an extra Ag-containing nanoparticle peak appeared at the low range of the NP size distribution histogram. This peak corresponds to Ag-containing particles that contain Ag mass equivalent to 25-30nm Ag nanoparticles (assuming spherical shape). However, the composition and the "real" size of these particles remains unknown as the particles may have formed from the in-situ reduction of dissolved silver or they originate from other processes involving nanocrystal formation, as has been shown to occur in sewage sludge, or interaction with natural organic matter. Overall, this study provides additional insight into the physicochemical mechanisms behind Ag nanoparticle behavior in marine media.

Environmental impact of engineered carbon nanoparticles: from releases to effects on the aquatic biota

Nano-ecotoxicology is an emerging science which aims to assess the environmental effect of nanotechnologies. The development of this particular aspect of ecotoxicology was made necessary in order to evaluate the potential impact of recently produced and used materials: nanoparticles (NPs). Among all the types of NPs, carbon nanoparticles (CNPs) especially draw attention giving the increasing number of applications and integration into consumer products. However the potential impacts of CNPs in the environment remain poorly known. This review aims to point out the critical issues and aspects that will govern the toxicity of CNPs in the environment.

Distribution behavior of superparamagnetic carbon nanotubes in an aqueous system

This study investigates the distribution behavior of superparamagnetic multiwalled carbon nanotubes (SPM-MWCNTs) in an aqueous system containing Lake Tai sediment. Specifically, the effects of dissolved organic matter (DOM) and sediment on SPM-MWCNTs under various conditions and the interaction forms between them were evaluated through a modified mathematical model and characterization. The results showed that DOM can stabilize SPM-MWCNTs by providing sterically and electrostatically stable surfaces, even under high sodium concentrations. The fitting accuracy of the Freundlich adsorption isotherm is higher than that of the Langmuir adsorption isotherm. Therefore, the adsorption of SPM-MWCNT on the sediment should proceed through a multiple, complex and heterogeneous adsorption mechanism. Characterization analyses indicated that DOM may serve as a bridge for the inorganic adsorption between SPM-MWCNTs and sediment. This study is the first to investigate the distribution behavior of magnetite coated carbon nanotubes (CNTs), which simplified the separation and quantification considerably. The findings of this study will serve as a valuable reference for future studies of magnetic CNTs.

Design Defines the Effects of Nanoceria at a Low Dose on Soil Microbiota and the Potentiation of Impacts by the Canola Plant

Soils act as nanoceria sinks via agricultural spreading and surface waters. Canola plants were grown for one month in soil spiked with nanoceria (1 mg·kg(-1)). To define the role of nanomaterials design on environmental impacts, we studied nanoceria with different sizes (3.5 or 31 nm) and coating (citrate). We measured microbial activities involved in C, N, and P cycling in the rhizosphere and unplanted soil. Bacterial community structure was analyzed in unplanted soil, rhizosphere, and plant roots by 454-pyrosequencing of the 16S rRNA gene. This revealed an impact gradient dependent on nanomaterials design, ranging from decreased microbial enzymatic activities in planted soil to alterations in bacterial community structure in roots. Particle size/aggregation was a key parameter in modulating nanoceria effects on root communities. Citrate coating lowered the impact on microbial enzymatic activities but triggered variability in the bacterial community structure near the plant root. Some nanoceria favored taxa whose closest relatives are hydrocarbon-degrading bacteria and disadvantaged taxa frequently associated in consortia with disease-suppressive activity toward plant pathogens. This work provides a basis to determine outcomes of nanoceria in soil, at a dose close to predicted environmental concentrations, and to design them to minimize these impacts.

Press or pulse exposures determine the environmental fate of cerium nanoparticles in stream mesocosms

Risk-assessment models indicate that stream ecosystems receiving municipal wastewater effluent may have the greatest potential for exposure to manufactured nanoparticles. The authors determined the fate of cerium oxide (CeO2 ) nanoparticles in outdoor stream mesocosms using 1) 1-time pulse addition of CeO2 nanoparticles, representative of accidental release, and 2) continuous, low-level press addition of CeO2 nanoparticles, representative of exposure via wastewater effluent. The pulse addition led to rapid nanoparticle floc formation, which appeared to preferentially deposit on periphyton in low-energy areas downstream from the location of the input, likely as a result of gravitational sedimentation. Floc formation limited the concentration of suspended nanoparticles in stream water to <5% of target and subsequent downstream movement. In contrast, press addition of nanoparticles led to higher suspended nanoparticle concentrations (77% of target) in stream water, possibly as a result of stabilization of suspended nanoparticles through interaction with dissolved organic carbon. Smaller nanoparticle aggregates appeared to preferentially adsorb to stream surfaces in turbulent sections, where Ce concentrations were highest in the press, likely a result of stochastic encounter with the surface. Streams receiving wastewater effluent containing nanoparticles may lead to exposure of aquatic organisms over a greater spatial extent than a similar amount of nanoparticles from an accidental release. Exposure models must take into account these mechanisms controlling transport and depositional processes.

Facet Energy and Reactivity versus Cytotoxicity: The Surprising Behavior of CdS Nanorods

Responsible development of nanotechnology calls for improved understanding of how nanomaterial surface energy and reactivity affect potential toxicity. Here, we challenge the paradigm that cytotoxicity increases with nanoparticle reactivity. Higher-surface-energy {001}-faceted CdS nanorods (CdS-H) were less toxic to Saccharomyces cerevisiae than lower-energy ({101}-faceted) nanorods (CdS-L) of similar morphology, aggregate size, and charge. CdS-H adsorbed to the yeast's cell wall to a greater extent than CdS-L, which decreased endocytosis and cytotoxicity. Higher uptake of CdS-L decreased cell viability and increased endoplasmatic reticulum stress despite lower release of toxic Cd(2+) ions. Higher toxicity of CdS-L was confirmed with five different unicellular microorganisms. Overall, higher-energy nanocrystals may exhibit greater propensity to adsorb to or react with biological protective barriers and/or background constituents, which passivates their reactivity and reduces their bioavailability and cytotoxicity.

Toxicity of CeO₂ nanoparticles on a freshwater experimental trophic chain: A study in environmentally relevant conditions through the use of mesocosms

The toxicity of CeO2 NPs on an experimental freshwater ecosystem was studied in mesocosm, with a focus being placed on the higher trophic level, i.e. the carnivorous amphibian species Pleurodeles waltl. The system comprised species at three trophic levels: (i) bacteria, fungi and diatoms, (ii) Chironomus riparius larvae as primary consumers and (iii) Pleurodeles larvae as secondary consumers. NP contamination consisted of repeated additions of CeO2 NPs over 4 weeks, to obtain a final concentration of 1 mg/L. NPs were found to settle and accumulate in the sediment. No effects were observed on litter decomposition or associated fungal biomass. Changes in bacterial communities were observed from the third week of NP contamination. Morphological changes in CeO2 NPs were observed at the end of the experiment. No toxicity was recorded in chironomids, despite substantial NP accumulation (265.8 ± 14.1 mg Ce/kg). Mortality (35.3 ± 6.8%) and a mean Ce concentration of 13.5 ± 3.9 mg/kg were reported for Pleurodeles. Parallel experiments were performed on Pleurodeles to determine toxicity pathways: no toxicity was observed by direct or dietary exposures, although Ce concentrations almost reached 100 mg/kg. In view of these results, various toxicity mechanisms are proposed and discussed. The toxicity observed on Pleurodeles in mesocosm may be indirect, due to microorganism's interaction with CeO2 NPs, or NP dissolution could have occurred in mesocosm due to the structural complexity of the biological environment, resulting in toxicity to Pleurodeles. This study strongly supports the importance of ecotoxicological assessment of NPs under environmentally relevant conditions, using complex biological systems.

Penetration and Toxicity of Nanomaterials in Higher Plants

Nanomaterials (NMs) comprise either inorganic particles consisting of metals, oxides, and salts that exist in nature and may be also produced in the laboratory, or organic particles originating only from the laboratory, having at least one dimension between 1 and 100 nm in size. According to shape, size, surface area, and charge, NMs have different mechanical, chemical, electrical, and optical properties that make them suitable for technological and biomedical applications and thus they are being increasingly produced and modified. Despite their beneficial potential, their use may be hazardous to health owing to the capacity to enter the animal and plant body and interact with cells. Studies on NMs involve technologists, biologists, physicists, chemists, and ecologists, so there are numerous reports that are significantly raising the level of knowledge, especially in the field of nanotechnology; however, many aspects concerning nanobiology remain undiscovered, including the interactions with plant biomolecules. In this review we examine current knowledge on the ways in which NMs penetrate plant organs and interact with cells, with the aim of shedding light on the reactivity of NMs and toxicity to plants. These points are discussed critically to adjust the balance with regard to the risk to the health of the plants as well as providing some suggestions for new studies on this topic.